Abstract: The bearing capacity of a pile group is inevitably effected by adjacent tunnel excavation. In this paper a centrifugal model test is described, and a back analysis of the mechanical and physical parameters of soils is conducted regarding test results and based on the displacement control method (DCM) for the ground loss ratio. Further analysis on some typical cases is performed by numerical simulation with respect to different relative positions between the tunnel and pile group. Results show that twin-tunnel excavation has obvious effects on the pile top settlement if the pile groups are all above the tunnel sides: for instance, the pile top settlement can reach 5.51% dp (diameter of a single pile) when the ratio of the overlying overburden depth (C) and tunnel diameter (D) is 3.7. When the tunnel bottom is flush with the pile bottom, the bearing capacity of the pile group increases after twin-tunnel excavation compared to that of a tunnel within the scope of the pile body and at the bottom of the pile end. The load transfer mechanisms of various piles of the pile group are similar to those of the friction and end bearing pile when the tunnel axis is within the scope of the pile body, while it is similar to the end bearing friction pile when the tunnel axis is be? low the pile end.